1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, a process for producing the electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are constituted basically of a photosensitive layer on which a latent image is formed by electrostatic charging and exposure to light and a substrate on which the photosensitive layer is provided.
Meanwhile, electrophotographic photosensitive members are required to have sensitivities, electric properties and optical characteristics in accordance with electrophotographic processes applied.
They are also required to have an environmental stability in any environment of from low temperature/low humidity to high temperature/high humidity which is good enough to enable them to perform well.
Faulty images are exemplified typically by image lines, black spots in white background areas, white spots in black background areas, background fog in white background areas, and also interference fringes caused by factors such as surface shape of substrates and uneven layer thickness of photosensitive members in the case of apparatus such as digital copying machines and laser beam printers in which exposure is effected using a light source having a single wavelength. Accordingly, in the manufacture of photosensitive members, some countermeasures must be taken in advance so that these faulty images do not occur.
As a factor having a great influence when such faulty images occur, there is the surface state of a substrate.
Substrates which are not treated at all after molding usually do not necessarily exhibit any surface state which is most suited for photosensitive members. Hence, problems caused by the untreated surface state may occur in many instances.
To solve such problems, methods of approach have hitherto been proposed, as exemplified by a method in which the surface of an aluminum substrate is subjected to chromating to form a chromated chemical conversion coating, as disclosed in Japanese Patent Application Laid-Open Nos. 54-12733 and 57-62056; a method in which a boehmite coating is formed on the surface of an aluminum substrate, as disclosed in Japanese Patent Application Laid-Open Nos. 58-14841 and 64-29852; and a method in which the surface of an aluminum substrate is oxidized by high-temperature treatment to form an oxidized film, as disclosed in Japanese Patent Application Laid-Open No. 57-29051.
With regard to, e.g., the method of chromating, substrates having a certain degree of performance can be obtained. However, since the treating solutions contain chromium, it is very difficult to dispose of waste liquor, and also this is not preferable in view of environmental safety.
With regard to the boehmite treatment, the crystal state of the surface can not be said to be suited for substrates of electrophotographic photosensitive members. They can be effective to a certain degree, with regard to electrophotographic performance, with regard to images, no satisfactory image quality has been achieved because the surface structure and shape are unsuited. Thus, under existing circumstances, those satisfying all performances have not been available.
What is aimed by the above surface treatment is that the film formed on the substrate surface prevents any non-uniformity from being caused in electrophotographic performances and images by electric charges injected locally from the substrate to the photosensitive layer.
As a method of preventing such local charge injection so as to prevent faulty images, a method is available in which the surface of an aluminum substrate is subjected to anodizing to provide a layer of aluminum oxide (e.g., Japanese Patent Application Laid-Open Nos. 2-7070 and 5-34964).
This method is a good method in order to maintain to attain such an aim. However, in order to form the layer uniformly without causing any uneven layer thickness on the substrate surface, the layer must be formed in a certain larger thickness, and a thickness of about 5 or 6 μm or more under usual conditions for its formation. Hence, the layer must be formed in a much larger thickness than the thickness actually required as a charge injection blocking layer, resulting in an increase in cost.